Flight control system automatic trim mechanism



Feb. 2, HUBBARD ETAL J 2,923,498

FLIGHT CONTROL SYSTEM AUTOMATIC TRIM MECHANISM Filed Dec. 26, 1956 2 Sheets-Sheet .1

m ravran. 5- 46/107! Wihf/ 1107/ 5 5 J/drrll 712/! fd/fsw/l/ 1% 2,923,498 FLIGHT CONTROL SYSTEM AUTOMATIC TRIM MECHANISM Filed Dec. 26. 1956 Feb. 2, RD ET AL 2 Sheets-Sheet 2 am e United States Patfi o FLIGHT CONTROL SYSTEM AUTOMATIC TRIM MECHANISM Herbert L. Hubbard, lnglewood, and Willis B. Morris, Hawthorne, Calif., assignors to Northrop Corporation, Hawthorne, Calif., a corporation of California Application December 2 6, 1956, Serial No. 630,575

6 Claims. (Cl. 244-76) The automatic trim mechanisms presently in use are actu-,

ated by a displacement of acomponent of the control sys-' tem. In other words, the automatic trim mechanism is energized when the force producer is displaced. Attention is directed to the fact that the diflerential of forces that occur in the cablecontrol system in the presently used mechanisms do not energize the automatic trim mechanism. Instead, displacement of the force producer, a result of system displacement, causes the actuation of the automatic tn'm mechanism. There are a number of reasons why the principle of displacement is not the ideal mechanical system, but one reason is that the diflerential of forces involved, in the cable control system do not actuate the trim mechanism despite the fact that these very forces are the reason a trim mechanism is required.

The invention to be considered herein deals directly with the forces involved and is not inhibited','restricted or unnecessarily influenced by the displacement of certain me chanical components. v A

An object of this invention is to provide an aircraft flight control system automatic trim' mechanism that .is'

energized by the diflerential of forces that occur in the cable control system as the result of displacement, to a new trim position of an aircraft controlsurface.

Another object ofthis invention is to provide an aircraft elevator flight control system automatic trim mechanism that includes a counter bob weight. This counter bob weight opposes operation of the automatic trim switch when the force producer bob weight imposes, as a result of acceleration influences, a differential-of forces in the cable control system. The force producer bob weight forces oppose over control, and the counter bob weight prevents such forces from actuating the automatic trim mechanism. 7

A yet further object of this'invention is to provide an aircraft flightl control system automatic trim mechanism that may be readily installed in an aircraft, economically fabricated, and easily maintained.

Figure 1 isia fragmentary, perspective view illustrating and having embodied therein the present invention.

Figure 2 is a view of a counter bob weight taken from Figure 1 looking in the direction of the arrow identified by the Numeral 2.

Figure 3 is a schematic illustration of a typical aircraft flight control system including the autopilot and illustrating the relationship of the present invention as it maybe applied and installed.

Referring to the drawings for a more detailed description of the present invention-llldesignates a pulley assembly including two rotatable cable pulleys. This pulley assembly which is spring loaded, may, for purposes of i1- Ice lustration only,be defined as a cable tension regulator. Threaded over each pulley is, for all intents and purposes an endless,cable 12. Additionally, the pulley assembly is mounted in such a manner that when a differential of force is established in the cable 12 they will pivot at 14 in the direction of the greatest force.

On the bracket 16, that connects the springs 18 of the pulleys, are a pair of ears 20 that receive a fitting 22.

A support mounting 24, of the type illustrated in Figure 1, is suitably'mounted on any convenient structure of the aircraft;

A pair of spaced apart, and parallel bracket tracks 26 and 27 having slots 28 and 29 therein are secured to the support. Mounted on each bracket track and in each slot,

for purposes of adjustment is a switch 30 and 31 respec-' tively. One. switch maybe designated as a down trim switch, 31, and one the up trim, 30, as indicated by the legend in Figure 3.

A boss 32 is provided on the support, and pivotally attached at 33'is an elongated lever or beam 34.' The beamextends between the switches 30 and 31 and that end of the beam opposed to the pivot 33 i d aspherical bean ing in fitting 22.. e V. l V

j A'second support mounting 36 is also attached to any convenient structure of the :aircraft. PivotaIly-attachedf at'38 to-the support is an L-shaped lever 40 having a.

weight 42 on one extreme end. The. opposed eirtrerne end ofthe lever 40 is attached to a link 44-tl1at is} in turn attached to one of the ears 20. I V 7 1 The weight 42 has an adapter 46 thereon that has a plurality of openings 48 therethrough which are'to receive of the spring its attached to the support 36. I V

Attention is directed to the schematic illustration of the flight control system depicted in Figure 3; It is to be one end of a compression spring 50. The opposite end understood that the illustrated structure is a mere representation of conventional and well known aircraft;com-

pone'nts.

A pilot stick 60 having a'quadrant' 62 thereon, inter mediate the ends, is connected to a reciprocable force producer 64. The force producer, as represented, for -purposes of convenience rides back and forth between rollers 66; trim actuator 68 is connected tortheforce. producer through the medium of a jack screw 70.

Also on the c'ontrolor'pilot stick 60 isa bob weight 72f that is influenced by accelerations that occur as the result of changes in the pitch attitude of the aircraft A series of pulleys 74 are located throughout the aircraft structure. and over and about these pulleys is thread-' ed cable 12. This cable 12 is, as previously stated, thread-. ed about pulley assembly 10. Further, between pulley assembly 10 and the control surface 76 is a final'or elevator quadrant 78. Between quadrant 78 and the control surface 76 and connecting the two together is a linkage system 80 that is representative of conventional equipment.

An autopilot 82, that may be considered a servo sys-.

tem, through the closed cable system 84, is also connected to the quadrant 78.

The control surface illustrated is the elevator, butit could also be the rudder, ailerons, or elevons.

- The various quadrants. and pulleys illustrated'along with the cables 12 and 84, as Well as the bob'weight 72 may be considered the cable control system/ The operation of the invention described is as followszl Assume the aircraft is flying on autopilot and it is desirable that it maintain straight and level flight.

As a result of some change that may occur dueto changes in flight characteristics, suchasthe consumptionie of fuel, it is necessary that the elevator be rotated about its axis to an up condition. The autopilot 82 receives" Fatente d F b. 2, 196d onthat part going from serribly 10 rotates about pivot 14..

moved in a direction toreduce the different force.

position ,the force arrows are: to be reversed. '7

msnt q ne tr -Po ti of an airqaft qntw r w V such a signal and throughthej-cable 84 rotates the quadrant 78 in th e direction indicated by thejforce arrow;

Further, assume that they cable 12'has under normal straight and level flight conditions; 1 0, pounds gf af o e; the pilot,stick-'.6 back 't Qzq a to change the attitude. of the surface 76 alichan e in,

forces occurs due to a displacement of thejforce pro duc er spring, in the cable 12, as indicated by the famous force arrows, It may, ,for purposesto f dlSCllSSlOIl, be as- 15 pounds of force; and that part back to the is reducedto 5 pounds. 7 it i As a result of these change .of forces ,the pulley as; This rotation ofthe pulley assembly 10 causes lever 3.4, to rotate resulting in, one switch,30, in thiscase. the up. trim. switch, gOII Ig tO thaup po tion .v Operation ofthe up. trim switch actuates the trim actuator. l s

When the change in the position of quadrant curs this changeis transmittedto thespringlof thetqfcei producer 64 and the spring is displacedin thedirec'ti ono'ff the arrows, resulting As the trim actuator is energized the forcepioducr l'cable As the difiere ntial" cable force is' i ernove d the cale-forces return to 10 pounds each,tthe pull ey.aslsegnil-. 0' rotates to the neutralp osition the .up ltrim switch movesto :the-otf position, and. the actuator isfd'e;

energized. In the event the surface 7 6 is to be-move d a down It maybe readily seen that the init'alobject otthis;

invention has been fulfilled and'th at there is provided a an aircraft flight. control systemgautornatic t'rirn mechathat is energized by differential f orcesflthat occurz in the cable control system as theiresu'lt ofidispl ace-l Now conslder the fact of the bob weightt7 2 whigh gets} prevent overcontrol in the pitch axis, and: the counter bob weight 42 and lever40, V p .I v e u t-gfia h nsesw tch:

An accelera Ion which a it of efi g r r f auses he'h h w ig t: 7 to produce a torque about its axis in a direction to oppose the pitch signal". This torque ;au ses-a;for :e r differential to occur in the cable 12 which normally would result in rotating the pulley assemblyy10 about pivot14, How; ever, as it is not desired to, trim out the bob weight ac-Q celeration ,forces, 'a counter bob weight 42 on lever 40 is so positioned with respect to the pulley assembly 10 and is rof such a weight as to counter thefo rcesthatf'arle imposed on the pulley assembly. In other, words, the;

differential of forces that are imposed'on thecables- 12 by the bob weight 72 tend to cause the pulley assembly 10 to rotateabout its axis in the same manner as if the; autopilot were, the cause. However, the counter bob weight42 is affected by the same cause that produced the torque from the bob weight 72, but ins'uch "amannerfas to resist the rotation of the pulley 10. As a'resultfthe.

pulley assembly '10 is not rotated, the trim factuat or is a difierential; load in tlliepfriables;

.trol system comprising a closed cable control system that is actuated by a servo system to cause a differential in i cable forces, a control surface, the attitude of which is altered by the servo system; a force producer into WhI Ch a force is urged, by the cable system when a diflerential 'of forces is. established; injthe latter; YQ-Ljpllllfil assembly l' 11f omthes'tick 60 has c A t. t s sume'd that that part of the cab r l trim the diiferentialofiforces out of the forcelproducer considered a part offfs'aidlcablesystem, that pivots when differential forces are establi s hed in said cable system; pivotal means interconnected to said pulley, assembly; and switches, adjacent to, actuated! bysaidllmeanskthat are connected to a trim' act uatorto actuate the' slame 'to system also. actuated pbyns aid servo system vtoscause a t force differential therein, a Iforce producerfac,

said cabletsystem, a trin-i actuatdr, and, a, system, ,automatic, trim], rnechanism comic, cable'pulley'sfthat are s s, of

l e ys; and atlast o e trim actuatorswitch'adiacentjand operated by said means to actuatefthe trimsac'tuatorlwhich,

' therein; acontrol surface, theiattitudeof v substantially fequali'zes' the iditferentia l, of forces sai cable system and'forceprodu'cera t 3. Trl' switch mechanis 'Jfor anaircraft flighteontmr system, comprising] a", closed cablej cb'liitrolp system: that actuated by a servo system to. cause adifleienfial ofiorces'f.

which is ead:

I i by the servofsystm'; a,forceiproducer intQfwhicha difier'i' ential of'fforces is urged; by the"cable;'system,fwherifla difierential of forces is establishedlinwthe latter;a pi'illeyf assembly] that-is a, par't o fsaid cable system, thatlpivo 'sL when fdifferential forces 'areest'ahlishedin said cable sjysi temjrpivo'tal means interconnected tosaidpul leyassembly'; switches adjacent .to. and: actuated by, said' "means, that re connected to a, trim actuator Qtofa'ctiiate .t he .same frfand' 1 trim the; differential; ofi fo'rces miter. thejforce'spr oducerl and cable. control system; a; b ob" weightlin thel cable control system that" is influenced 'by acceler tons w c are, t

due to .a'changew in pitch attitude of the zinc aft toimpose is actuated'by servo system cau s that aa p rt Qfs d ab e-sy t m; th t-vitae whe .t a e hh ssht a, 4 Trim switch mecha srn fortan aircraft fl ight control system comfil'isirig fclosed cable cont ljsystemth t -t e e l e h hrf e t e? A h altered Y' V9JY 5w%iQWQPEQQPWP a ar i .1. r 3.-- h a l t m w en; ash tch a q qr y es ab s e -t el ter; ai ley. as m,

i ,t V 1" ential'forces areestablishedin said cable systemypiyotal;

adiagfifllt to-ja tu ted b a d means; h t. are o nectedr to a-trim' actuator to actuatethe sameto trim the differ: ential of forces out of theiorce producer and cable con;

. trol systempand a pivotal bob weight-interconnected to said q a rant tha rcs and m a ele ationr j t-.- p d on s d Pu l y s aih1y opr yent e a tqr 0 V caus n o e atio ot hcH m-ac u tor- 5. Trim switch mechanism for an alrc ra ft fliight control y s isinea p osed able htra sys em-that is i .i mrthatgivqt 'whqa lifierentia tar ets a' e 'esta lished ia said c'abl ej coiitr :l syste and which pivot when said force. difljerential' t" lished therein; pivotal rrieans intercoh'riectedgfd Saul 1P said cable system; pivotal means interconnected to said pulley assembly; switches, adjacent to and actuated by said means, that are connected to a trim actuator to actuate the same to trim the dilferential of forces out of the force producer and cable control system; and an element interconnected to said pulley assembly that prevents pitch acceleration forces from operating the trim mechanism.

6. Trim switch mechanism for an aircraft flight control system comprising a closed cable control system that is actuated by a servo system to cause a differential of forces therein; a control surface, the attitude of which is altered by the autopilot; a force producer into which a differential of forces is urged, by the cable system, when a differential of forces is established in the latter; a pulley assembly of connected cable pulleys that are a part of said cable system, that pivot when differential forces are established in said cable system; pivotal means interconnected to said pulley assembly; switches, adjacent to and actuated by said means, that are connected to a trim actuator 6 to actuate the same to trimthe differential of forces out of the force producer and cable control system; a principal bob weight in the cable control system that is influenced by accelerations due to changes in pitch attitude of v the aircraft to impose a diiferential of forces in said cable system independent of as well as concurrently with said servo system; and an element interconnected to said pulley assembly that resists the principal bob weight forces imposed on said pulley assembly, and prevents a reduction of the diiferential of forces established by said principal bob weight.

References Cited in the file of this patent UNITED STATES PATENTS Bonsteel Dec. 4, 1956 

